NANOSCALE PHENOMENA IN SURFACE ELECTROCHEMISTRY - SOME INSIGHTS FROM SCANNING-TUNNELING-MICROSCOPY AND INFRARED-SPECTROSCOPY

Examples of nanoscale phenomena at electrochemical interfaces, examine d recently in our laboratory by means of in-situ scanning tunneling mi croscopy (STM) and infrared reflection-absorption spectroscopy (IRAS), are discussed with the overall objective of assessing some spheres of applicability of these approaches for exploring substrate and adlayer atomic-/molecular-level properties which propagate over nanoscale dis tances. While the direct spatial structural information obtainable by in-situ STM makes this technique of obvious importance for exploring n anoscale phenomena, the infrared probe offers not only chemical specif icity, but also the fast (similar to 10(-11) s) spectral timescale ena bles fluxional adlayer structures to be probed. Four types of applicat ions along these lines are considered. First, recent STM evidence for adsorbate-induced nanoscale restructuring on ordered monocrystalline e lectrodes is discussed, specifically for Pt(100) and Au(110) surfaces. The occurrence of restructuring with retention of the substrate unit cell (i.e. without reconstruction) is outlined. Apparent similarities in the long-range Br-induced restructuring observed on Au(110) with th e adsorbate-induced reconstruction of (110) surfaces in UHV are also n oted. Second, the likely occurrence of CO-induced reconstruction of Pd (110) electrodes, as probed by IRAS, is described as an example of the value of spectral comparisons between electrochemical and UHV systems for elucidating surface structure in the former environment. Third, t he utility of dipole-dipole coupling analysis for elucidating the nano scale spatial structure of both CO adlayers and metal substrates is di scussed. The specific topics chosen, CO islands formed during adlayer electrooxidation and the microscopic nature of Pt/Ru alloy catalysts, illustrate the usefulness of such analyses in both ordered monocrystal line and polycrystalline surface environments. Lastly, applications of UHV-based IRAS measurements for exploring double-layer charge-solvent interactions are briefly outlined. The results uncover a long-range i nfluence of ionic charge upon inner-layer solvent orientation and also clarify the roles of the solvent molecules in curtailing short-range ion-adlayer interactions and screening the otherwise-complex electrost atic-field effects upon adsorbate vibrational properties. (C) 1998 Pub lished by Elsevier Science Ltd. All rights reserved.